Wireless communication tends to be generalized in the apparatuses forming part of our everyday life, and these are in particular the apparatuses and devices designed for the public.
In this respect, the quick development of the wireless communication protocol known as Bluetooth® is particularly illustrative.
Bluetooth® is a low-power, short-range wireless networking standard designed for local area voice and data transfer. Bluetooth® is a packet-based protocol which relies on a master-slave communication model. In this model, one master may communicate with up to 7 slaves in a piconet, both master and slave devices sharing the same channel and a same clock of the master. The master controls formation of Bluetooth® communication links and procedures with slaves. Thus, a slave may transmit only after being polled by the master, that is, the medium access control lies with the master. Both master and slaves may transmit on available slots, as defined by the master's Bluetooth® clock. Time may be divided into slots of 625 μs (microseconds) in the piconet. The master and the slave thus transmit packets alternatively, and the packet may be of length 1, 3 or 5 slots. The master and slaves in the piconet may alternate transmission time using a time-division multiplexing. A time-division-duplex (TDD) emulates full duplex communication over a half duplex communication link.
Bluetooth® supports voice and data traffics. The data traffic is given a best effort service while the voice traffic is given a guaranteed service and is allocated 64 Kbps bandwidth. Three kinds of radio communication links are supported between a master and a slave: synchronous Connection-Oriented (SCO), enhanced synchronous Connection-Oriented (e-SCO) and asynchronous Connection-less (ACL). SCO link reserves or allocates predetermined time slots on the time axis. In practice, an SCO link is used for transporting voice traffic. ACL link randomly uses time slots on the time axis for communications, and it is typically used for transporting data traffic.
The SCO link defined in the Bluetooth® specification provides a full-duplex symmetric 64 Kbps link between the master and a slave with reserved time slots. The master transmits SCO packets in reserved master-to-slave SCO slots to the slave at regular SCO interval, and the slave is allowed to respond with SCO packets in reserved slave-to-master SCO slots. No SCO packet retransmission occurs over the SCO link. The SCO packets are typically used for 64 kb/s speech transmission with a fixed payload length of 240 bits.
Enhanced SCO (eSCO) link provides greater flexibility than SCO link in setting up link Indeed, eSCO allows retransmission mechanisms to achieve reliability, and also a wider variety of packet types, and greater intervals between packets than SCO, thus increasing radio availability for other links. Further, eSCO includes a CRC (Cyclic Redundancy Check) as part of the audio data packet to allow error detection and a re-transmission request, higher data rates by using packets that span more than 1 timeslot, and allows asymmetric links to allow high quality audio to be streamed in one direction.
Bluetooth® supports voice traffics so that this protocol can be used for transmitting voice during a telephone call. For instance, a Bluetooth® headset may act as a slave connected to a cell phone having Bluetooth® capabilities and acting as master. Voice may be transmitted from the headset to the cell phone (and inversely) on a symmetric link with reserved channel bandwidth and regular periodic exchanges of data representing the voice traffic in the form of reserved slots.
Transmitting voice data is particularly power consuming, both for the Bluetooth® headset and for the cell phone point of view. As energy saving is critical for operation life of battery of electronic mobile communication devices using Bluetooth® and reduction of energy consumption of these devices is currently a major concern, there is a need for a solution permitting to reduce the energy consumption of a device using a Bluetooth® radio link connection for transmitting voice traffic.